Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $209.79   9.674%   $230.0851   $230.09   $230.10   $230.10  
  Purchase #2 $207.51   4.190%   $216.2047   $216.20   $216.20   $216.20  
  Purchase #3 $58.52   8.477%   $63.4807   $63.48   $63.50   $63.50  
  Purchase #4 $149.25   11.355%   $166.1973   $166.20   $166.20   $166.20  
  Purchase #5 $76.44   13.423%   $86.7005   $86.70   $86.70   $86.70  
  Purchase #6 $231.63   3.392%   $239.4869   $239.49   $239.50   $239.50  
  Purchase #7 $43.40   11.219%   $48.269   $48.27   $48.25   $48.30  
  7 purchase totals = $976.54       $1,050.4242   $1,050.43   $1,050.45   $1,050.50